The present invention relates to a method and apparatus for separating gaseous effluent from carbon fibers in a vapor grown carbon fiber manufacturing process, and more particularly, to a method and apparatus which allows gaseous effluent to be separated from carbon fibers without diluting the effluent.
Vapor grown carbon fibers and carbon nanofibers (both referred to herein as xe2x80x9ccarbon fibersxe2x80x9d) are widely used as a high-performance material for composites due to their high strength and high modulus. Such fibers are typically formed in a gas phase reaction in a reactor by forming a gaseous mixture which may comprise a gaseous hydrocarbon, ammonia, and a compound decomposable to form nuclei. The mixture is heated in the reactor for a time and temperature sufficient to decompose or pyrolyze the decomposable compound to form catalytic nuclei which induce growth of carbon fibers, which fibers are subsequently recovered from the reactor in a collection chamber
The apparatus for manufacturing vapor-grown carbon fiber from gas phase compounds and gas entrained catalyst particles generally includes horizontal reactors in which fiber is produced, flow meters to regulate gas flow, furnaces to supply the energy for reaction, and fiber collection chambers to separate the fiber from the gas effluent. See, for example, U.S. Pat. Nos. 5,374,415, and 5,024,818, the disclosures of which are hereby incorporated by reference. The fiber collection chamber, or disengager, typically utilizes settling tanks and filters to separate the hot, combustible, gaseous effluent from the solid carbon fiber product. The hot, combustible gaseous effluent is then cooled to near ambient temperature and large amounts of air are added so that the concentration of the combustible gas is well below the lower explosive limit. The settling tanks are sufficiently large to reduce the effluent gas velocity below that which can suspend fiber. However, no attempts have been made to process the gaseous effluent for reuse. It would be advantageous to be able to recycle the gaseous effluent for use as a feedstock material or heating source and to be able to separate the gaseous effluent into its constituents such as hydrogen, methane, ethane, etc.
Accordingly, there is still a need in the art for a method for separating carbon fiber from gaseous effluent during the fiber manufacturing process which allows the gaseous effluent to be reused.
The present invention meets that need by providing a method of separating carbon fibers from gaseous effluent during fiber production which allows the effluent to be reused. The invention utilizes a collection chamber designed to separate the carbon fiber from the hot, combustible gaseous effluent without diluting the effluent.
According to one aspect of the present invention, a method for separating gaseous effluent from carbon fibers is provided. The method comprises providing a collection chamber containing a gaseous effluent and carbon fibers which have been formed by a continuous gas phase reaction. The collection chamber includes top and bottom portions and includes exit tubes affixed to the bottom portion of the chamber.
The carbon fibers are removed from the collection chamber by compressing the carbon fibers from the bottom portion of the chamber into the exit tubes such that the compressed carbon fibers form an airtight seal, thus preventing the escape of said gaseous effluent from said chamber. The seal also prevents air from entering the chamber which could dilute the gaseous effluent, rendering it unsuitable for reuse. As the carbon fibers are continually forced into the exit tubes, they are eventually displaced such that they can be collected from the opposite end of the tubes into bundles
The collection chamber of the present invention preferably includes a top portion and a bottom portion, where the top portion includes an opening for receiving vapor grown carbon fibers and gaseous effluent from one or more reactors which are connected to the chamber. The bottom portion includes a chamber for collecting fibers dropping from the top portion. Exit tubes are affixed to the bottom portion of the chamber for receiving carbon fibers. The chamber further includes a piston affixed to the bottom portion for compressing carbon fibers accumulated in the bottom portion into the exit tubes. The collection chamber preferably further includes an outlet to allow removal of the gaseous effluent from the chamber. The gaseous effluent may then be recycled for use and otherwise separated into its constituents for reuse.
Accordingly, it is a feature of the present invention to provide a method and apparatus for separating gaseous effluent from vapor grown carbon fibers which allows the gas to be reused. This, and other features and advantages of the present invention, will become apparent from the following detailed description, the accompanying drawings, and the appended claims.